The present invention concerns an industrial robot or so-called manipulator which is arranged, with the aid of a programme control, to repeat automatically a pattern of movements which the robot, operated manually has performed once. It is primarily intended for surface coating operations but may also be used for other purposes, such as polishing, grinding and the like, and in all operations where it is desired to repeat a movement pattern in an identical manner and a number of times.
Teaching of the movement is effected by running the tool attachment and thus also all the movable parts of the robot manually through the movement pattern.
The tool attachment which is provided with a so-called hand, is capable of performing three movements (turning in two different planes which are at right angles to one another, and rotation, simulating the possibilities of movement of the human hand). The tool, e.g. a spray gun, is secured in the tool attachment. The detailed design of the "hand" does not form part of the present invention and consequently will not be described in detail herein.
When the robot is to be programmed, e.g. for spray painting, the spray painter moves the gun in the desired movement pattern during the painting of the article and during this operation the movements of the "hand" and the arm system are registered in the memory of the control system. It is thereafter possible to paint identical articles in an automatic manner with the aid of the control system thus programmed.
In order to prevent that the task of the operator is unnecessarily disturbed or hampered during the programming proper by the large weights that need to be handled and by the resistance to movement inherent in the arm system itself, the weight of the latter must be balanced and the resistance to movement in joints and drive means be kept at a low level. The balancing of the arm system is in the present case effected by spring means.
When the arm system, thus blanced, is moved through the movement pattern by the operator, the hydraulic cylinders which drive the arm system during the automatic operation, will take part in the movement during the programming. The cylinders in themselves exhibit frictional resistance in gaskets and similar means, in addition to which the displacement of the oil quantities in the cylinders means further resistance. It is alreadly known to reduce the latter resistance by providing the hydraulic cylinders with a so-called by-pass valve which hydraulically short-circuits the hydraulic connections to the various cylinders during the programming operation.
This reduces the work to transfer of the oil quantity from the piston to the piston rod side and vice versa and to "dumping" (discharge) and replenishing, respectively, to or from the tank in question of the small quantity of oil which constitutes the volumeric difference between the piston and piston rod sides.
This principle is applied also to the robot in accordance with the present invention which is of the kind comprising a bracket which is arranged to turn relative to a support, a pivotally mounted crane boom the lower end of which is journalled on a horizontal shaft on said bracket, a jib one end of which is pivotally mounted about a horizontal shaft at the upper end of the crane boom, said jib supporting a tool attachment, a hydraulic cylinder arranged between the bracket and the crane boom to effect the pivotal movement of the crane boom in a vertical plane and a hydraulic cylinder inserted between the crane boom and the jib to pivot the jib in the same vertical plane, and a device comprising a spring means to balance the crane boom and the jib. This principle has, however, been found insufficient as the resistance to movement still is too strong.